In recent years, electronic devices such as mobile information devices and information home appliances are becoming more sophisticated in functionality along with advancement of digital technology. Along with the more sophisticated functionality of the electronic devices, miniaturization and speed-enhancement of the semiconductor devices used in the electronic devices have been rapidly advanced. Among all, demand for nonvolatile memories with a large capacity represented by flash memories is expanding rapidly.
In addition, research and development of a nonvolatile memory device which uses a so-called variable resistance nonvolatile memory element has been advanced, the nonvolatile memory device being a new nonvolatile memory of the next generation which replaces the flash memory. Here, the variable resistance nonvolatile memory element is an element having a characteristic that a resistance value changes reversibly by electrical signals and being capable of storing data corresponding to the resistance value in a nonvolatile manner.
In order to make a variable resistance nonvolatile memory element switchable between a high resistance state and a low resistance state under application of electrical pulses, it is necessary to perform an electrical operation called forming. The forming herein refers to application of a voltage (forming voltage) higher than a normal write voltage to the variable resistance nonvolatile memory element having an extremely high resistance value after manufacture.